Method and apparatus for attenuating a light beam

ABSTRACT

A light valve for attenuating a collimated light beam contains a focusing lens, a light vane and motor control. The focusing lens contains a focal length and lens diameter. The focusing lens focuses a collimated light beam to generate a light cone such that the dimensions of the light cone are based on the diameter and focal length of the focusing lens. The light vane deflects light within the light cone. The motor is controlled to position the light vane to attenuate the light within the light cone by placing the light vane in at least one position ranging from a zero stop attenuation position to a full stop attenuation position. For a single degree of light vane rotation into the light cone, the light beams is attenuated by three percent. In the zero stop position, the light vane is parallel to an edge of the light cone so that no light is attenuation. In the full stop position, the light vane is located thirty degrees, relative to the zero stop position, into the light cone.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of image processing systems,and more particularly, to conversion of motion picture film to a highdefinition video format.

2. Art Background

Telecine systems have been developed for converting motion picture filmimages into conventional NTSC and PAL video signal formats.Traditionally, these telecine systems were developed to convert themotion picture film images to television signals for broadcast. Prior tothe emergence of solid state imagers, telecine equipment was constructedusing camera tubes or flying-spot scanners. The flying-spot scannergenerates a video signal from film by scanning the film image with avery small spot of light and collecting the resulting transmitted lightat a photo cell. Although an effective means to convert film to NTSC orPAL video signal formats, flying spot scanners generate video signalswith limited resolution. Therefore, flying spot scanners are not aneffective means for film to high definition video conversion. Asequipment such as telecines are developed to facilitate the interfacebetween high definition video and film, it is important to address allaspects of the system interface to provide quality film to highdefinition video conversion.

In general, telecine systems generate light to create optical filmimages from devices known as lamphouses. Traditionally, lamphouses fortelecines and optical printers utilize specular light sources. Thespecular light sources, in conjunction with reflector and condensinglens types, are typified by high efficiency and contrast. Althoughspecular light sources and the associated optics exhibit high efficiencyand contrast, the specular light sources require critical opticalalignment of lamp filament, reflector and condensing lenses. Thiscritical alignment also varies with magnification further emphasizingthe need for precise optical alignment. Additionally, a specular sourceincreases the visibility of surface abrasions on the film.

The color television cameras used in traditional telecine systemstypically have spectral sensitivities and pre-amplifier gaincharacteristics optimized for a 2900° K. to 3200° K. light source. Theselight sources, such as tungsten light sources often used in televisionstudios, are appropriate for the spectral sensitivities of the Vidicontype detectors. However, a high definition charged coupled device (CCD)camera has different spectral characteristics than the Vidicon typedetectors. The spectral sensitivity of present CCD detectors ischaracterized by poor blue sensitivity and excellent red sensitivityinto the infra-red region. Therefore, in telecine systems utilizing CCDdetectors, it is desirable to provide a light source in the lamphousethat provides efficient alternatives to traditional tungsten lightsources by exhibiting spectral bandwidths and color temperaturesmaximized for the CCD detector.

A television camera often contains an optic prism to separate the inputpolychromatic optical image into its three constituent monochromaticcomponents of red, green and blue (RGB). Existing color televisioncamera prism designs make a very efficient use of the available lightspectrum. Typical prism designs result in greater than 80% of thespectral bandpass being directed to the appropriate red, green or bluedetector. Unfortunately, the separation into the RGB components in theprism results in a certain amount of crosstalk between the RGBdetectors. In order to reduce or eliminate the effects of the crosstalkamong the CCD detectors, a matrix is required in the television camerasignal processing circuit. Although the matrix helps to reduce oreliminate the CCD detector crosstalk, it results in a reduction of thesignal to noise performance of the system. Therefore, it is desirable togenerate a light source that minimizes the crosstalk among CCD detectorsso as to reduce or eliminate the need for the crosstalk matrix.

Color film emulsions suffer from a similar crosstalk problem. In fact,the problem is more severe since the dyes generated in the film emulsionhave considerably inferior bandpass characteristics to that of theinterference filters employed in television camera prisms. However,color negative films employ a very efficient photo-chemical matrix or"dye masking" system which results in excellent color response whichenables color print film colorimetry to exceed the present displaycolorimetry of high definition video signals (HDVS). When color filmemulsions are the originating source for HDVS images, an appropriatecolor separation system is required which is substantially differentfrom that of a color television camera imaging the real world. The mostimportant characteristic of this separation system is that it createscolor separations based on the primary analysis characteristics of thefilm emulsion while minimizing electrical crosstalk, and thereforereducing the magnitude of matrix coefficients.

An appropriately designed lamphouse can contribute to overall systemperformance by providing optimal conditions to realize best signal tonoise performance. Therefore, it is desirable to create a lamp housethat provides a light source designed to compliment the scanner spectralcharacteristics, minimize crosstalk among the color channels, andprovide an even light field which can reduce shading compensation.

Conventional motion picture film consists of frame images which arecommonly displayed sequentially at a rate of 24 frames per second (fps).However, the standard video frame rate is 25 video fps for PAL formatvideo, 29.97 video fps for the NTSC video format and 30 video fps forthe SMPTE-240M high definition video format. Therefore, to convertmotion picture film images into video image signals, frame conversion isrequired. In PAL systems, it is a universal practice to reproduce the 24frame rate film at 25 fps. In practice, this is acceptable because thediscrepancy is only 4.17%, and the increase in pitch and reduction inrunning time of the film is acceptable. In the case of NTSC and highdefinition video, the discrepancy of 6 frames per second is a 25%difference, and therefore, reproducing the 24 fps motion picture filmwould be intolerable. To compensate for the frame rate mismatch, atechnique commonly referred to as 3-2 pull down in used to generatehigher video frame rates.

Typically, the 3-2 video frames are generated by holding the film in aprojector gate to permit two field exposures or three field exposures tooccur. A pulldown mechanism, which transports the film into theprojector gate, delivers the film at uneven periods in order to generateeither the two or three exposures. In addition, the pulldown mechanismsused to achieve the 3-2 film frame to video frame conversion are edgeguided. The edge guided system does not provide accurate imageregistration. While edge guiding may provide acceptable results for NTSCand PAL video conversion, a highly accurate positioning pulldownmechanism is required for high definition video. Therefore, it isdesirable to generate the 3-2 pulldown film to video frame conversionrate with the same high precision frame placement system in which theoriginal image was created on the camera.

SUMMARY OF THE INVENTION

A real-time telecine system for converting motion picture film to highdefinition video is disclosed. The telecine system contains a controlunit comprising a database which provides complete control over allparameters associated with the film to high definition video conversion.In a preferred embodiment of the present invention, the telecine systemconverts motion picture film images displayed at 24 frames per second toSMPTE-240M high definition video displayed at 30 frames per second. Ingeneral, the telecine system comprises a film transport sub-system,camera sub-system, rotating shutter and lamphouse. To convert a motionpicture film to high definition video, the motion picture film isadvanced, by the film transport sub-system, a single frame at a timeduring a pulldown period, and the film is held steady during a registerperiod.

The lamphouse contains three monochromatic light sources wherein eachlight source is controlled independently by the control unit. Theindependent control of each monochromatic light source permits variablelight intensity outputs from each light source. To expose a film frameto the camera sub-system, the three monochromatic light sources areintegrated to generate a single diffused light source. The diffusedlight illuminates the film frame to generate an optical film image, andthe rotating shutter permits exposure of the optical film image to thecamera sub-system in a 3-2 pulldown arrangement. The camera sub-systemcontains a correction lens and a high definition (HD) camera. Theoptical film image is projected onto a mirror which transfers theoptical image to the correction lens. The correction lens performsoptical corrections on the optical film image caused by aberrations froman optical prism in the HD camera. The HD camera comprises three highdefinition charged coupled device (CCD) arrays for image detection.

Each of the three monochromatic light sources contains a light valve.The control unit controls the light intensity output for each of thethree monochromatic light sources through control of the light valve.The light valve contains a focusing lens, a light vane and motorcontrol. The focusing lens contains a focal length and lens diameter.The focusing lens focuses a collimated light beam from a monochromaticlight source to generate a light cone such that the dimensions of thelight cone are based on the diameter and focal length of the focusinglens. The light vane deflects light within the light cone. The motor iscontrolled to position the light vane to attenuate the light within thelight cone by placing the light vane in at least one position rangingfrom a zero stop attenuation position to a full stop attenuationposition. For a single degree of light vane rotation into the lightcone, the light beams is attenuated by approximately three and a thirdpercent. In the zero stop position, the light vane is parallel to anedge of the light cone so that no light is attenuation. In the full stopposition, the light vane is located thirty degrees, relative to the zerostop position, into the light cone. The positioning of the light vanemay be calibrated such that the motor control positions the light vanein f-stop increments.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects features and advantages of the present invention will beapparent from the following detailed description of the preferredembodiment of the invention with references to the drawings in which:

FIG. 1 illustrates a front right perspective view of a telecineconfigured in accordance with the present invention.

FIG. 2 illustrates a plain view of a lamphouse configured in accordancewith the present invention.

FIG. 3 illustrates a single light source and an integrating sphereconfigured in accordance with the present invention.

FIG. 4 illustrates the spectral characteristics for dichroic filtersconfigured in accordance with the present invention.

FIG. 5 illustrates a top view of a light valve, a lens configuration,and a spherical integrator configured in accordance with the presentinvention.

FIG. 6 illustrates a front right perspective view of the sphericalintegrator configured in accordance with the present invention.

FIG. 7 illustrates the prior art concept of 3-2 pulldown for film tovideo conversion.

FIG. 8 illustrates a front right perspective view of a rotating shutterconfigured in accordance with the present invention.

FIG. 9 illustrates a plain view of a rotating shutter incorporating theteachings of the present invention.

FIG. 10 illustrates a portion of a film transport system configured inaccordance with the present invention.

FIG. 11 illustrates a corrective lens and camera system configured inaccordance with the present invention.

FIG. 12 illustrates a functional block diagram of a control unitconfigured in accordance with the present invention.

FIG. 13 illustrates a control unit interface configured in accordancewith the present invention.

NOTATION AND NOMENCLATURE

Some portions of the detailed descriptions which follow are presented interms of algorithms and symbolic representations of operations. Thesealgorithmic descriptions and representations are the means used by thoseskilled in the art to most effectively convey the substance of theirwork to others skilled in the art. An algorithm is here, and generally,conceived to be a self consistent sequence of steps leading to a desiredresult. These steps are those requiring physical manipulations ofphysical quantities. Usually, though not necessarily, these quantitiestake the form of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It provesconvenient at times, principally for reasons of common usage, to referto these signals as bits, values, elements, symbols, characters, images,terms, numbers, or the like. It should be borne in mind, however, thatall of these and similar terms are to be associated with the appropriatephysical quantities and are merely convenient labels applied to thesequantities.

The present invention relates, in part, to method steps for a controlunit to generate other desired physical signals. The present inventionalso relates to apparatus for performing these operations. Thisapparatus may be specially constructed for the required purposes, or itmay comprise a general purpose computer selectively activated orreconfigured by a computer program stored in the computer. Thealgorithms, methods and apparatus presented herein are not inherentlyrelated to any particular computer. In particular, various generalpurpose machines may be used with programs in accordance with theteachings herein, or it may prove more convenient to construct morespecialized apparatus to perform the required method steps. The requiredstructure for a variety of these machines will appear from thedescription given below. Machines which may perform the functions of thepresent invention include those manufactured by Sony Corporation ofAmerica, as well as other manufacturers of control systems.

DETAILED DESCRIPTION OF THE INVENTION

A method and apparatus for a real-time film to video conversion systemis disclosed. In the following description, for purposes of explanation,specific nomenclature is set forth to provide a thorough understandingof the present invention. However, it will be apparent to one skilled inthe art that these specific details are not required in order topractice the present invention. In other instances, well known circuitsand devices are shown in block diagram form in order not to obscure thepresent invention unnecessarily.

Referring to FIG. 1, a front right perspective view of a telecineconfigured in accordance with the present invention is illustrated. Atelecine 100 is shown coupled to a control unit 110. The control unit110, operating in conjunction with the telecine 100, provides completecontrol for all parameters associated with the film to high definitionvideo conversion. The operation of control unit 110 is described morefully below. In a preferred embodiment of the present invention, thetelecine 100 converts motion picture film images to SMPTE-240M highdefinition video. However, the teachings of the present invention couldalso be applied to other telecine systems. For example, the telecine 100may be configured to convert motion picture film to either NTSC or PALstandard video formats without deviating from the spirit or scope of theinvention. Generally, the telecine 100 converts motion picture filmimages displayed at 24 frames per second to SMPTE-240M high definitionvideo displayed at 30 frames per second.

The telecine 100 contains a film transport sub-system 120, a camerasub-system 135, a rotating shutter 130 and a lamphouse 125. To convert amotion picture film to a video, the motion picture film, such as film115 shown in FIG. 1, is coupled to the film transport sub-system 120.The film transport sub-system 120 moves the motion picture film 115 suchthat the film frames are exposed to the camera sub-system 135. Apulldown period occurs for each motion picture frame wherein the film ismoved into a register position. A register period is defined as theperiod in which the film is held steady in the register position. Thelamphouse 125 generates a diffused light source illuminating the filmimage on film 115 during exposure periods specified by the rotatingshutter 130. During the exposure period, the diffused light illuminatesthe film image to generate an optical film image. The camera sub-system135 contains a correction lens 145 and a high definition (HD) camera150. The optical film image is projected onto a mirror 140. The mirror140 transfers the optical image to the correction lens 145. Thecorrection lens 145 performs optical corrections on the optical filmimage caused by aberrations in HD camera 150. The HD camera 150comprises three high definition charged coupled device (CCD) arrays forimage detection. In a preferred embodiment of the present invention, theHD camera 150 comprises a Hyper HAD™ CCD array. The optical film imageis recorded in the HD camera 150.

Referring to FIG. 2, a plain view of a lamphouse configured inaccordance with the present invention is illustrated. The lamphouse 125contains, in part, three light sources 200, 205 and 210, and anintegrating sphere 240. Each of the light sources 200, 205 and 210generates a collimated light beam. The light sources 200, 205 and 210contain a non-incandescent lamp such as fluorescent, HMI, CID, CSI orxenon. The CCD arrays in HD camera 150 have different spectralcharacteristics than tube type pick-up detectors. The spectralsensitivity of present CCD detectors is characterized by poor bluesensitivity and excellent red sensitivity into the infra-red region ofthe spectrum. The non-incandescent light sources have much highercorrelated color temperatures than tungsten light sources, and thenon-incandescent light sources provide a better blue output than thetungsten light sources. Consequently, in telecine systems utilizing CCDdetectors, light sources comprising non-incandescent lamps provide moreefficient light sources than traditional tungsten light sources.

The light sources 200, 205 and 210 contain lamps 204, 208 and 214respectively. In a preferred embodiment of the present invention, thelamps 204, 208 and 214 are xenon lamps. The xenon lamps output acollimated light beam which consists of a constant color temperatureafter a specified burn in period regardless of the current supplied tothe lamp. The light sources 200, 205 and 210 also contain variable powersupplies 202, 206 and 212, respectively. The variable power supplies202, 206 and 212 are all coupled to a power source (not shown) and tothe control unit 110. In addition, light sources 200, 205 and 210contain light valves 218, 222, and 226, respectively. The light valves218, 222, and 216 attenuate light output from the corresponding lamp204, 208 and 214. A detailed description of the operation of the lightvalves 218, 222 and 226 is provided below.

The collimated light output generated in each of the lamps 204, 208 and214 is transmitted through a corresponding lens configuration 216, 220and 224. The lens configurations 216, 220, and 224 filter the light fromeach corresponding lamp. The output from each of the three lamps isfiltered to a specific bandwidth in order to generate threemonochromatic light sources. In the preferred embodiment of the presentinvention, the light sources are separated into green, red, and bluelight sources. However, other complimentary color combinations can beused, such as the color trio of cyan, magenta, and yellow, with equaleffectiveness. The three monochromatic light sources are input to theintegrating sphere 240. The monochromatic light sources are mixed orcombined in the integrating sphere 240. The output of the integratingsphere 240 is a highly diffused polychromatic light source. Theintegrated polychromatic light source is used to generate the filmoptical image.

Referring to FIG. 3, a single light source and an integrating sphereconfigured in accordance with the present invention is illustrated. Forpurposes of explanation, only a single light source 205 is illustratedin FIG. 3 although the lamphouse 125 of the present invention comprisesthree such light sources. The light sources 200, 205 and 210 differ onlyin the spectral characteristics of the corresponding lensconfigurations. The light source 205 contains a lamp 208 coupled to avariable power supply 206. The variable power supply 206 supplies powerto the lamp 208 at a constant voltage but at variable currents. Adecreased output in current from the variable power supply 206 resultsin a linear attenuation of the light output from lamp 208.

In order to control the light intensity output from lamp 208, thevariable power supply 206 receives an analog control signal from controlunit 110 ranging from 0 to 5 Volts. When control unit 110 supplies a 5volt control signal to the variable power supply 206, the variable powersupply 206 supplies a maximum current output to the lamp 208. However,when less than a 5 volt control signal is provided from control unit 110to the variable power supply 206, the variable power supply 206 suppliesa decreased amount of current to the light source 208. The 0-5 voltcontrol range is linear such that the analog control voltage input tovariable power supply 206 is directly proportional to the lightintensity output from light source 208. In the present invention, theattenuation of the light output from control of the variable powersupply is limited to 50% attenuation.

The collimated light generated from each light source is transmittedthrough a corresponding lens configuration. As shown in FIG. 3, thelight valve configuration 220 comprises a heat mirror 306, threedichroic filters 307, 308 and 309, and a focusing lens 310. Thecollimated light output from lamp 208 first passes through the heatmirror 306 to reduce the temperature of the light. The light transmittedthrough each heat mirror is then passed through the three dichroicfilters. For the single light source illustrated in FIG. 3, the threedichroic filters are designated 307, 308 and 309. The dichroic filters307, 308 and 309 filter light from light source 205 to obtain desiredspectral characteristics for the light.

Referring to FIG. 4, spectral characteristics for dichroic filtersconfigured in accordance with the present invention is illustrated. Thespectral responses 400, 410 and 420 for the three sets of dichroicfilters contained in light sources 200, 205 and 210 are shown.Specifically, FIG. 4 depicts the percentage of light transmittance as afunction of the wavelength of the light incident on each set of dichroicfilters. The spectral response 400 represents the spectralcharacteristics required to generate the light source for the bluemonochromatic channel, and the spectral response 410 represents thespectral characteristics required to generate the light source for thegreen monochromatic channel. The spectral response 420 represents thespectral characteristics required to generate the light source for thered monochromatic channel. However, the particular spectral responsecharacteristics for a set of dichroic filters is dependent on thespectral sensitivity for the detector device used in the telecinesystem. For the preferred embodiment of the present invention, spectralresponses 400, 410 and 420 depict the optimal spectral characteristicsfor the dichroic filters for use with the Hyper HAD™ CCD arrays. Thedichroic filters 307, 308 and 309 are intended to represent a broadcategory of optical filters which are well known in the art and will notbe described further.

The three collimated monochromatic light sources output from the threesets of dichroic filters are each input to a focusing lens. The focusinglenses for each of the three lamps in lamphouse 125 are identical.Referring again to FIG. 3, a focusing lens 310 is shown for the singlelight source 205. Each focusing lens shapes the input light to generatea point source for attenuation by a corresponding light valve and forsubsequent input to the integrating sphere 240. In the preferredembodiment of the present invention, the focusing lens for each lightsource, such as focusing lens 310, comprises an aspheric lens having a30 mm diameter and a 25 mm focal length. In a preferred embodiment ofthe present invention, the focusing of the light source from focusinglens 310 results in a one eighth inch beam. However, as one skilled inthe art will recognize, the actual optical characteristics for thefocusing lens is dependent upon the optical light path, the light valveand the integrating sphere utilized for the particular telecine system.

Still referring to FIG. 3, a light valve 222 for the light source 205 isshown. The light valves 218 and 226 are identical to light valve 222.For the light source 205 shown in FIG. 3, the light valve 222 contains alight vane 245, a stepper motor 252 and a microstep drive 254. Themicrostep drive 254 is coupled to the stepper motor 252, and the steppermotor is connected to the light vane 245 via a bracket 247. Each lightvane comprises a radius and a height. The microstep drive 254, and inturn the stepper motor 252, are controlled by a control pulse from thecontrol unit 110, and the control pulse determines the amount ofmovement for a shaft on the stepper motor 252. The light vane isconstructed of beryllium copper. The placement of the light vane 245 inthe optical path of the light source permits a full range of lightattenuation. The light valve 222 also comprises a position sensor 250.The position sensor 250 provides feedback for reset and position controlof light vane 245.

In operation, a control pulse is provided from control unit 110 tomicrostep drive 254. The microstep drive 254 then controls the movementof stepper motor 252 to position light vane 245. The stepper motor maybe controlled to provide any number of discrete positions for light vane245. The control unit 110 transmits the control pulse to the microstepdrive 254 when the telecine is in the pulldown period. Because thepulldown period is short for the real time telecine system of thepresent invention, the final positioning of each light vane must occurrapidly. The positioning of each light vane exhibits a fast responsetime ranging from 5 ms for full light to zero light output attenuationto 5 microseconds (us) for a 6 decibels (dB) light output attenuation.For the real time telecine system of the present invention, the lightvane 245 is only moved during the pulldown period. The light vane 245need only move thirty degrees for full light attenuation, and thereforethe time limitation for positioning the light vane during the pulldownperiod is achievable. Although use of a stepper motor in the presentinvention results in a maximum response time of approximately 5 ms, alow inertia servo-motor could improve the response time an order ofmagnitude.

In the telecine system of the present invention, each light output maybe attenuated through control of both the variable power supply and thelight valve for the corresponding lamp. The control of the variablepower supply results in response times for attenuation of the lightoutput three orders of magnitude faster than the response time from thelight valve configuration. However, as discussed above, attenuation oflight by the variable power supply is limited to 50% attenuation.Therefore, the control unit 110 integrates the control of the variablepower supply and the light valve configuration to achieve desired lightintensity outputs for color corrections. The majority of colorcorrections is achieved by control of the variable power supply for theappropriate light source. However, when the required light attenuationfor the proper color correction exceeds the 50% limitation, the controlunit 110 controls the light valve configuration to attenuate the lightoutput for large increments exceeding the attenuation limitation of thevariable power supply. For fine adjustments of light attenuation betweenthe large increments, the control unit 110 controls the variable powersupply to attenuate the light output the desired level. The combinationof the variable power supply control and the light valve configurationcontrol ensures the best median response time for a required change incolor balance.

Referring to FIG. 5, a top view of a light valve, a lens configuration,and a spherical integrator configured in accordance with the presentinvention is illustrated. The light vane 245 illustrated in FIG. 5 islocated outside the optical path of the light source. When light vane245 is located in this position, the light source output from focusinglens 310 is unattenuated. However, movement of light vane 245 thirtydegrees from the initial position, as shown by the arrow in FIG. 5,results in complete attenuation of the light beam. In the preferredembodiment of the present invention, the focusing lens 310 generates afocal plane of light comprising a 25 mm. wide collimated beam, and thelight vane 245 comprises a 12 mm. radius. The light valve configurationof the present invention exhibits a linear response such that rotationof the light vane 245 into the light beam focal plane results in lightmodulation which is essentially linear with respect to the angle ofrotation. The linear relationship between the position of the light vaneand the amount of attenuation provides for simplified control by thecontrol unit 110. Specifically, rotation of the light vane 245 into thefocal plane of light results in approximately 3.33% attenuation of lightoutput for every 1 degree of rotation. The height of light vane 245affects both the response time for positioning the light vane 245 andthe resolution of the light output.

Referring to FIG. 6, a front right perspective view of the integratingsphere 240 configured in accordance with the present invention isillustrated. The integrating sphere 240 comprises three entrance ports620, 630 and 640. The integrating sphere 240 also comprises an exteriorcylindrical shell 600 and an inner sphere 610. Located at the top ofintegrating sphere 240 is an exit port 650. The light from eachmonochromatic light source is input into the inner sphere 610 throughone of the entrance ports. The entrance ports are located sixty degreesrelative to the internal sphere 610. Each monochromatic light sourceenters a corresponding entrance port and an integrated and diffusedlight source is generated at exit port 650. In a preferred embodiment ofthe present invention, the entrance ports comprise a 1 inch diameter,and exit port 650 comprises a 1.5 inch diameter. The port wall comprisesan area between inner sphere 610 and outer cylinder 600, and isapproximately 0.25 inches thick. The integrating sphere 240 is intendedto represent a broad category of optical mixers, such as an integratingsphere used in goniophotometry, which are well known in the art and willnot be described further.

The lamphouse of the present invention contributes to overall systemperformance by providing optimal conditions to realize best signal tonoise performance. The independently adjustable dichroically filterednon-incandescent light sources provide the optimal spectral quality forvarious detector response characteristics. The integrating sphere takesinput from the light sources and generates a highly-diffused integratedlight source that reduces or eliminates the CCD detector crosstalk andprovides an even light field that can reduce shading compensation. Inaddition, the lamphouse of the present invention provides a separationsystem that creates color separations based on the primary analysischaracteristics of the film emulsion. Therefore, the lamphouse alsoreduces the magnitude of the film masking matrix coefficients resultingin better signal to noise performance. The lamphouse of the presentinvention also has application for use in an additive light valve filmprinter and sequential film scanners. In addition, the lamphouse can beused as a replacement for subtractive light sources used in opticalprinters.

Referring to FIG. 7, the prior art concept of 3-2 pulldown for film tovideo conversion is illustrated. On a top portion of FIG. 7, input filmframe images from a conventional motion picture film are sequentiallylabeled. Immediately below the film frame images, are video field imagesfor which conversion from the motion picture film to video is desired.For purposes of explanation, the video frame images may comprise eitherNTSC or SMPTE-240M high definition video. As can be seen from FIG. 7,input film frame image 700 is exposed in three different video periodsto generate video field images 720, 730, and 740. This results in videofield images 720, 730 and 740 comprising film frame image 700. For filmframe image 710, two video field images 750 and 760 are exposed withfilm frame image 710. The process of exposing three video fields for afirst film frame image, and two video fields for a subsequent frameimage is repeated.

Referring to FIG. 8, a front right perspective view of a rotatingshutter configured in accordance with the present invention isillustrated. In a preferred embodiment of the present invention, therotating shutter 130 provides exposure periods for frame conversion ofmotion picture film displayed at 24 fps to SMPTE-240M high definitionvideo displayed at 30 fps. The rotating shutter 130 comprises a discrotated by a motor, wherein the disc comprises five shutter aperturessuch that five video fields are exposed in one revolution of the disc.To expose the five fields of video per rotation, the rotating shutter130 comprises shutter apertures 800, 810, 820, 830 and 840. Each shutteraperture permits exposure for one field of video, and the apertures areseparated by 49, 49, 72, 78, and 92 degrees respectively.

The rotating shutter 130 is mounted to a central hub 850 via threebushings 845. A shaft 852 couples the rotating shutter 130 to a steppermotor 854. The stepper motor 854 is coupled to a microstep drive 856,which in turn is controlled by the control unit 110. The mounting ofrotating shutter 120 to the central hub 850 is non-rigid. The steppermotor 854 provides torque at uneven amounts which is an undesirablecharacteristic attributable to stepper motors. Due to the uneven torque,the rotating shutter 130 must be mounted loosely in order to spin ataccurate rates. The mounting configuration, including the rubber mountedcentral hub 850, allows the outer perimeter of rotating shutter 130 tobe slightly loose. The control unit 110 provides control to microstepdrive 856, which causes stepper motor 854 to rotate the rotating shutter130 at 720 revolutions per minute (rpm). The control of the steppermotor 854 is described more fully below in conjunction with adescription of the control unit 110.

Referring to FIG. 9, a rotating shutter incorporating the teachings ofthe present invention is illustrated. A film aperture 900 comprises anarea within the pulldown mechanism in which each frame of the motionpicture film sequentially passes. When the telecine system is in theregister period, one frame of the motion picture film is located exactlywithin the dimensions of the film aperture 900. FIG. 9 also illustratesthe five shutter apertures 800, 810, 820, 830 and 840. In operation, therotating shutter 130 rotates at 720 rpm. When one of the shutterapertures passes over the film aperture 900, the integrated diffusedlight source from the integrating sphere 240 is permitted to passthrough the shutter aperture to project the integrated light through thefilm frame located within the within the dimensions of film aperture900. A polychromatic optical film image is thus projected from the filmframe to the mirror 140.

For purposes of explanation, FIG. 9 illustrates a number of crossedportions within the rotating shutter 130. The crossed triangularportions 910, 940, 950, 975 and 985 graphically represent a periodrelative to the rotation of the rotating shutter 130 in which HD camera150 is in a vertical blanking period. The vertical blanking periodspecifies the time in which accumulated charge is transferred out of theHD CCD arrays, and consequently an exposure of a film frame in the HDcamera 150 can not occur during vertical blanking. The larger crossedtriangular regions 920 and 970 represent a period relative to therotation of the rotating shutter 130 in which the telecine system is inthe pulldown period. The time required for pulldown is no longer thanthe time required to rotate the rotating shutter 62 degrees. Asdiscussed above, the pulldown period is the time at which the filmtransport sub-system moves the film for placement of the next framewithin the film aperture 900. The exposure of an optical film image ontothe HD camera 150 cannot occur during the pulldown because the filmframe is not stable. Therefore, in order to properly transfer the filmto video in a 3-2 pulldown transfer arrangement, the exposure of theoptical film image must occur outside both the pulldown period and thevertical blanking period. As shown in FIG. 9, the rotating shutter 130exposes the film frame in a period outside both the HD camera verticalblanking period and the telecine system pulldown period.

The present invention employs a pin registration system that registerson the perforations of the film in the same manner that the originalmotion picture camera registered on the film. The pin registrationsystem is described more fully below in conjunction with a descriptionof the pulldown mechanism. Because the telecine system of the presentinvention converts film to high definition video, such an accurate filmtransport system is required. The pin registration system requires thatthe pulldown of the film occur in constant intervals. As shown by thecrossed triangular portions 920 and 970 in FIG. 9, the pulldown periodfor the telecine system of the present invention occurs at constantintervals. The constant or even pulldown periods permit the use of a pinregistration system to provide the accurate positioning of the filmframes. Therefore, the 3-2 pulldown required for film to high definitionvideo conversion is generated by varying when the exposures to thecamera occur.

As shown in FIG. 9, after the pulldown period 920, the shutter apertures800, 810 and 820 expose a single film frame to generate three videofield images. After the pulldown period 970, the shutter apertures 830and 840 expose the next film frame to generate two video field imagesfrom the single film frame. Therefore, the present invention, comprisingpulldown periods in constant intervals, generates the 3-2 conversion bycontrolling when the exposures of the film frames to the HD cameraoccur. As an alternative to the rotating shutter 130 of the presentinvention, generation of the 3-2 conversion by varying when theexposures occur may be accomplished through control of the electronicshutter in the HD camera 150.

In a preferred embodiment of the present invention, each portion of theoptical frame image is exposed to the HD camera 150 for 2 ms. Althougheach portion of the optical film image will only be exposed to the HDcamera for 2 ms, a 4 ms period is required to expose the entire opticalfilm image for each film frame. For example, shutter aperture 800located at 52 degrees on the rotating shutter 130 begins exposure of afirst portion of an optical image as shutter aperture 800 passes underthe film aperture 900. In 2 ms after the beginning of the exposure, theshutter aperture 800 is located exactly over film aperture 900. In thenext 2 ms, the shutter aperture 800 continues to pass over the filmaperture 900, resulting in exposure of a latter portion of the opticalfilm image. The pulldown periods 920 and 970 illustrated in FIG. 9provide a worst case scenario for the time required for actual pulldown.In practice, the pulldown period may occur in only 90 degrees ofrotation of the rotating shutter. However, the 124 degrees of rotationfor the pulldown period takes into account any vibrational shock causedfrom the stop and start of the film by the film transport sub-system. Inaddition, the 124 degree pull down period also considers the time forpin registration in the film transport sub-system.

Referring to FIG. 10, a portion of a film transport system configured inaccordance with the present invention is illustrated. The film transportsub-system 120 comprises a supply sprocket 1000, a pulldown mechanism1010, and a take-up sprocket 1020. The supply sprocket 1000 and take-upsprocket 1020 are coupled to stepper motors 1030 and 1050, respectively.The pulldown mechanism 1010 contains a center sprocket and is coupled toa servo motor 1040. The stepper motors 1030 and 1050, and the servomotor 1040 are coupled to control unit 110. The control unit 110provides film transport control signals or pulses trains to drive therotation of stepper motors 1030 and 1050 such that the film istransferred at 24 fps. The control of servo motor 1040 and steppermotors 1030 and 1050 is described more fully below.

The pulldown mechanism 1010 controls the accurate movement of the motionpicture film during the pulldown period and holds the film steady duringthe register period. In order to insure accurate pulldown such that theouter perimeters of one film frame exactly reside in the film aperture900, the pulldown mechanism 1010 employs a pin registration system. Thepin registration system, driven by the servo motor 1040, registers onthe perforations in the same manner that the motion picture cameraregistered on the film to create the original image. The pulldownmechanism 1010 also contains an encoder coupled to the shaft of theservo motor 1040. The encoder counts the number of revolutions of theshaft on the servo motor 1040. The shaft revolution count is transmittedto the control unit 110. The control unit 110 utilizes the count tocontrol the supply and take-up sprockets 1000 and 1020 as is explainedmore fully below. The encoder contained in pulldown mechanism 1010 isintended to represent a broad category of encoding devices, such as anoptical encoding device, which are well known in the art and will not bedescribed further.

Referring to FIG. 11, a corrective lens and camera system configured inaccordance with the present invention is illustrated. The optical filmimage is reflected from the mirror 140 and input to the correction lens145 as shown by the light path in FIG. 11. The correction lens 145performs optical corrections on the optical film image, and thecorrected optical film image is then input to the HD camera 150. The HDcamera 150 comprises prism optics which separate the polychromaticoptical film image into its constituent monochromatic film images. Eachmonochromatic film image is then projected onto a high density CCDarray. The optical corrections performed in the correction lens 145correct for spherical and axial color aberrations caused by the prismoptics in HD camera 150. The lens configuration to obtain the desiredoptical correction is dependent upon the prism for the particular cameraused in a telecine system. The correction lens 145 is intended torepresent a broad category of optical correction devices which are wellknown in the art and will not be described further.

The correction lens 145 is mounted on a lens adjustable mount 1105, andthe HD camera 150 is mounted on a camera adjustable mount 1110. Anadditional correction lens 1100 is also mounted on the lens adjustablemount 1105. The lens adjustable mount 1105 is coupled to three steppermotors X_(m) 1116, Y_(m) 1114 and Z_(m) 1112, and the camera adjustablemount 1110 is coupled to three motors X_(m) 1130, Y_(m) 1125, and Z_(m)1120. All six motors are controlled remotely from the control unit 110.Each set of the three motors controlling the positioning of lensadjustable mount 1105 and the camera adjustable mount 1110 adjust therespective mount in one physical dimension. The motor controlledadjustable mounts 1105 and 1110 permit precise optical alignment fromthe control unit 110.

The X_(m) motors 1116 and 1130 and the Y_(m) motors 1114 and 1125provide the ability to position the optical film image onto the opticalcenter of the HD CCD arrays. In addition, the X_(m) motor 1116 and theY_(m) motor 1114 move the lens adjustable mount to pan and scan theoptical film image in the X and Y dimension. The pan and scan operationadjusts the X and Y positioning of the optical film image on a scene byscene basis to compensate for the proportional differences betweenmotion picture film frame dimensions and video frame dimensions. TheZ_(m) motors 1112 and 1120 move the lens adjustable mount 1105 and thecamera adjustable mount 1110 respectively in a Z dimension to adjust themagnification of the optical film image projected on the HD camera 150.After the proper magnification is achieved, the Z_(m) motor 1120 movesthe Z dimension of the camera adjustable mount to focus the optical filmimage in the HD camera 150.

In a preferred embodiment of the present invention, during an initialset-up period, the corrective lens 145 and the HD camera 150 arepositioned to focus the film optical image on the optical center of theHD camera 150. After the initial positioning, only the lens adjustablemount is adjusted for the pan and scan operation because the correctionlens 145 is lighter and easier to control than the HD camera 150. Inreality, movement of the correction lens 145 for the pan and scanoperation does not change the optical centers enough to warrantreadjustment. The X_(m) and Y_(m) motors 1130 and 1125 are provided forcompleteness allowing three dimensional position control of the HDcamera 150.

Referring to FIG. 12, a functional block diagram of a control unitconfigured in accordance with the present invention is illustrated. In apreferred embodiment of the present invention, the control unit 110comprises an IBM™ compatible personal computer system. Although acomputer system is disclosed, the control unit 110 may comprise anydevice capable of performing the functions described below. FIG. 12conceptually illustrates the major components for a typical computersystem which may comprise the control unit 110. The control unit 110comprises a central processing unit (CPU) 1200, and a memory 1210. TheCPU 1200 and memory 1210 are coupled to an I/O subsystem 1220. The I/Osubsystem 1220 is coupled to a mass memory device 1225 and a pluralityof external devices. It will be appreciated that additional devices maybe coupled to the control unit 110 for storing data, such as magnetictape drives, buffer memory devices and the like. The mass memory device1225 may store data and programs for the control and operation of thecontrol unit 110. The control unit 110 also comprises a display monitor1230. A cursor control device is provided through a touch screen on thedisplay monitor 1230. These major components of control unit 110 arethose typically found in most computers and, in fact, the control unit110 is intended to be representative of a broad category of dataprocessing devices.

Referring to FIG. 13, a control unit interface configured in accordancewith the present invention is illustrated. In general, the control unitinterface 1300 is part of the I/O subsystem 1220 and contains aplurality of peripheral interface devices for controlling the telecine100. In addition, the control unit interface 1300 receives input from adatabase 1235 and a control panel 1240. Specifically, the control unitinterface 1300 comprises a synchronization card 1305, four dual channelserial interface cards 1310, 1315, 1320 and 1325, a six channel digitalto analog (D/A) converter 1330, and two motor control cards 1335 and1340. All of the interface devices on the control unit interface 1300may be accessed and controlled by the CPU 1200.

In general, the synchronization card 1305 generates clocking and timingsignals for operation in conjunction with the control unit 110. Thesynchronization card 1305 receives a high definition video sync input(HD Sync In) signal. The HD Sync In may be generated from the video syncsignal in the HD camera 150. In a preferred embodiment of the presentinvention, the HD Sync In signal is generated by a precision highdefinition video sync source to provide accurate synchronization of allhigh definition video components. In general, the synchronization card1305 generates a plurality of derivative frequencies based on the HDSync In. In this way, the synchronization card 1305 provides timingsources which are locked to the precision high definition video syncsignal. The generation of derivative frequencies, which are phase lockedto a primary frequency, from a primary frequency, such as the HD SyncIn, is well known in the art and will be not be described further.

The serial interface cards 1310 and 1315 are coupled to a plurality ofmulti-media resources. Specifically, a first channel of the serialinterface card 1310 is connected to a high definition video taperecorder 1345. A second port of the serial interface card 1310 iscoupled to an audio source 1350. The serial interface card 1315 has botha first and second port coupled to audio sources 1355 and 1360. Theserial interface card 1320 is coupled to the high definition camera 150.The serial interface card 1320 receives a high definition video syncsignal from the synchronization card 1305 or from a precision timesource. The precise high definition video sync signal is synchronized tothe video sync signal in the HD camera 150. In this way, completesynchronization is achieved between the high definition video syncsource, the control unit 110 and the HD camera 150. The serial interfacecard 1325 is capable of receiving data from the database 1235 and thecontrol panel 1240. The control panel 1240 provides the ability for auser to control the multi-media resources coupled to the control unit110. The utilization of the database 1235 is described more fully below.

Three channels of the six channel D/A converter 1330 are coupled to thelamphouse 125. The three channels of the D/A converter 1330 output theanalog control voltage that determines the amount of current output fromeach power supply in the three monochromatic light sources. Toaccomplish this task, the CPU 1200 drives the D/A converter 1330 tooutput three analog signals ranging from 0 to 5 volts. The threechannels of the D/A converter 1330 are independently controlled.Therefore, the control unit 110 may set the power level of eachmonochromatic channel separately and independently. The control of eachvariable power supply is linear such that the input analog voltageapplied corresponds to the output current supplied to the correspondinglamp. The light intensity output may be attenuated approximately onestop. The generation of the analog control voltage for control of thelamphouse power supplies is discussed more fully below in conjunctionwith calibration of the control unit 110.

The control unit interface 1300 also contains S1 and S2 motor controlcards 1335 and 1340. The S1 motor control card 1335 controls X_(m) 1116,Y_(m) 1114, and Z_(m) 1112 for movement of the lens adjustable mount1105. The S1 motor control card 1335 generates a pulse frequency tocontrol the positioning of the lens adjustable mount 1105. The S1 motorcontrol 1335 also controls X_(m) 1130, Y_(m) 1125, and Z_(m) 1120 formovement of the camera adjustable mount 1110. The S2 motor control card1340 controls six stepper motors and one servo motor. Specifically, theS2 motor control card 1340 controls the stepper motors in each lightvalve 218, 222 and 226. The S2 motor control card 1340 generates a pulsefrequency proportional to the amount of movement desired for thecorresponding light vane. The S2 motor control card 1340 transmits thepulse frequency to the light valves 218, 222 and 226 only during thepulldown period of the telecine. In addition, the light valveconfigurations 218, 222 and 226 are controlled independently such thateach light vane within a corresponding light valve configuration may beset to a different position.

The S2 motor control card 1340 controls the movement of supply sprocket1000, take up sprocket 1020 and pulldown mechanism 1010. A filmtransport frequency derived from the synchronization card 1305 issupplied to the S2 motor control card 1340. Consequently, the filmtransport frequency is locked to a derivative of the video syncfrequency. The locking of the video sync frequency to the film transportfrequency permits control of the film transport sub-system relative totelecine system operation. As discussed above, an encoder is coupled tothe shaft of the servo motor 1040 for generating a count. The count isfed back to control unit 110, and is used to stop and start the centersprocket in the pulldown mechanism 1010. In addition, the count is alsoused to control the supply and take-up sprockets 1000 and 1020. Theservo motor 1040 permits a fine degree of control in the stopping pointof each succeeding tooth on the center sprocket. In addition, thecontrol and operation of pulldown mechanism 1010 permits the filmtransport sub-system 120 to operate at a wide range of speeds. Theintermittent film transport system 120 and the S2 motor control cardprovide optimal performance for accurate placement of film frames.

The S2 motor control card 1340 also controls the rotation of rotatingshutter 130. A rotating shutter frequency, derived from thesynchronization card 1305, is supplied to the S2 motor control card1340. The rotating shutter frequency is used to generate shutter controlpulses to drive the stepper motor 854 for rotation of the rotatingshutter 130 at 720 rpm. By using a derivative frequency to control thestepper motor 854, the rotation of the rotating shutter 130 isphased-locked to the HD Sync In signal. The synchronization of therotating shutter frequency and the HD Sync In insures that shutterapertures 800, 810, 820, 830 and 840 expose the optical film images tothe HD camera 150 at the appropriate times. The integrity of the timingfor exposure periods generated by the rotating shutter 130 is alsoinsured by tracking the rotating shutter via an open loop controlsystem. The open loop control system of the S2 motor control card 1340counts the shutter control pulses transferred to micro step drive 856.The rotating shutter count is normalized to the HD Sync In signal todetect any drift from the shutter control pulse with the HD Sync Insignal. If the count comparison indicates that the shutter control pulseis driving the rotating shutter 130 is too fast or slow, then the pulsefrequency for subsequent shutter control pulses transmitted to therotating shutter 130 is compensated accordingly.

The telecine system of the present invention is initially calibratedsuch that the lamphouse 125 illuminates the film image at desired levelsof light intensity. The initial calibration session correlates valuesgenerated from the control unit 110 to a specific light intensity outputfrom the lamphouse 125. In a preferred embodiment of the presentinvention, the light intensity values are calibrated to an absolutescale so as to match "F-stop" values provided on a motion picture filmcamera. The control unit 110 interface permits the user to enter a valueon a scale ranging from 0-50 for each monochromatic channel. Whenconverting a motion picture film to HD video, a cinematographer sets thelight intensity for a scene corresponding to a desired light levelthrough the system interface of the control unit 110. The value for thelight intensity settings is stored in database 1235. Subsequently, thevalue may be retrieved for film to video conversion. In addition tolight intensity settings, the positioning for the correction lens 145and the HD camera 150, as well as other camera setup parameters arestored in database 1235.

The telecine system of the present invention operations in conjunctionwith a color corrector system. In general, the color corrector systemperforms various transforms to correct for film and video signalcharacteristics. In correcting for the film characteristics, the colorcorrector system performs film masking matrix processing whichcompensates in each monochromatic channel for crosstalk amongpolychromatic color emulsions of the original film stock. In addition,the color corrector system performs characteristic curve processing foreach channel in accordance with a Hurter-Driffield characteristic curve.The Hurter-Driffield characteristic curve depicts the relationshipbetween the film dye density and a logarithm of the relative filmexposure such that the color corrector system considers gamma, minimumand maximum film dye densities and shadow and highlight compression. Thevideo signal characteristics include electronic channel cross talk andnon-linear responses. For a detailed description of a color correctionsystem for use in conjunction with the telecine system of the presentinvention see U.S. patent application Ser. No. 07/710,704, filed on Jun.5, 1991, entitled Digital Color Correction System and Method, assignedto the assignee of the present invention, Sony Corporation of America,Park Ridge, N.J., now U.S. Pat. No. 5,255,083.

In a preferred embodiment of the present invention, the color correctionparameters associated with the film are stored in the database 1235. Thecolor correction parameters for the film are used as an initial startingpoint for the calibration of the telecine system. The telecine system ofthe present invention provides complete control over all aspects of thefilm to high definition video conversion, and therefore the telecinesystem generates a HD video output that maintains the integrityassociated with the initial color correction parameters. Subsequently,in the color correction phase, the initial color correction values canbe used as absolute values for performing the color correctionfunctions. Therefore, traditional altering of the adjustments for colorcorrection based on subjective criteria is replaced with a moreobjective analytical approach so that the integrity of the colorcorrection values is maintained throughout the film to video conversion.

Although the present invention has been described in terms of apreferred embodiment, it will be appreciated that various modificationsand alterations might be made by those skilled in the art withoutdeparting from the spirit and scope of the invention. The inventionshould therefore be measured in terms of the claims which follow.

What is claimed is:
 1. An apparatus for attenuating a light beamcomprising:focusing means for generating a cone shaped light beam fromsaid light beam, said focusing means comprising a diameter and a focallength wherein outer perimeters of said cone shaped light beam areconfigured in accordance with said diameter and said focal length; lightvane means for deflecting at least a portion of said cone shaped lightbeam, said light vane means comprising a face having a height and awidth, said height being at least equal to said diameter of saidfocusing means; and positioning means coupled to said light vane meansfor positioning said light vane means within the cone shaped light beamto attenuate said cone shaped light beam, said positioning means placingsaid light vane means in at least one position ranging from a zero stopposition to a full stop position, said face of said light vane meansbeing parallel to an edge of said cone shaped light beam and said widthof said face extending to a focal point of said cone shaped light beamfor said zero stop position and said face of said light vane being 30degrees into said cone shaped light beam relative to said face in saidzero stop position for said full stop position.
 2. The apparatus forattenuating the light beam as claimed in claim 1 wherein said light vanemeans is constructed of beryllium copper.
 3. The apparatus forattenuating said light beam as claimed in claim 1 wherein placement ofsaid light vane means by said positioning means results in approximatelythree and a third percent light attenuation for a single degree of lightvane rotation into said cone shaped light beam.
 4. The apparatus forattenuating the light beam as claimed in claim 1 wherein saidpositioning means comprises control means for controlling saidpositioning means, said control means specifying a position ranging fromsaid zero stop position to said full stop position for said light vanemeans and said positioning means placing said light vane means in saidposition.
 5. The apparatus for attenuating the light beam as claimed inclaim 4 wherein said control means further comprises stop setting meansfor positioning said light vane means so as to attenuate said coneshaped light beam in f-stop increments.
 6. An apparatus for attenuatinga light beam comprising:a focusing lens for generating a cone shapedlight beam from said light beam, said focusing lens comprising adiameter and a focal length wherein outer perimeters of said cone shapedlight beam and focal point of said cone shaped light beam are configuredin accordance with said diameter and said focal length of said lens; alight vane for deflecting at least a portion of said cone shaped lightbeam, said light vane comprising a face having a height and a width,said height being at least equal to said diameter of said focusing lens;and a motor coupled to said light vane for positioning said light vanewithin the cone shaped light beam to attenuate said cone shaped lightbeam, said motor placing said light vane in at least one positionranging from a zero stop position to a full stop position, said face ofsaid light vane being parallel to an edge of said cone shaped light beamand said width of said face extending to said focal point of said coneshaped light beam for said zero stop position, and said face of saidlight vane being 30 degrees into said cone shaped light beam relative tosaid face in said zero stop position for said full stop position.
 7. Theapparatus for attenuating the light beam as claimed in claim 6 whereinsaid light vane is constructed of beryllium copper.
 8. The apparatus forattenuating said light beam as claimed in claim 6 wherein placement ofsaid light vane by said motor results in approximately three and a thirdpercent light attenuation for a single degree of light vane rotationinto said cone shaped light beam.
 9. The apparatus for attenuating thelight beam as claimed in claim 6 wherein said apparatus furthercomprises a control unit coupled to said motor for controlling placementof said light vane, said control unit generating a pulse frequencyspecifying a position ranging from said zero stop position to said fullstop position for said light vane such that said motor places said lightvane in said position.
 10. The apparatus for attenuating the light beamas claimed in claim 9 wherein said control unit further comprises stopsetting values for generating said pulse frequency for positioning saidlight vane so as to attenuate said cone shaped light beam in f-stopincrements.
 11. A method for attenuating a light beam comprising thesteps of:focusing said light beam in accordance with a diameter and afocal length to generate a cone shaped light beam from said light beam;providing a light vane for deflecting at least a portion of said coneshaped light beam, said light vane comprising a face having a height anda width, said height being at least equal to said diameter; andpositioning said light vane within the cone shaped light beam toattenuate said cone shaped light beam by placing said light vane in atleast one position ranging from a zero stop position to a full stopposition, said face of said light vane being parallel to an edge of saidcone shaped light beam and said width of said face extending to a focalpoint of said cone shaped light beam for said zero stop position andsaid face of said light vane being 30 degrees into said cone shapedlight beam relative to said face in said zero stop position for saidfull stop position.
 12. The method for attenuating the light beam asclaimed in claim 11 wherein said step of providing a light vanecomprises the step of providing a light vane constructed of berylliumcopper.
 13. The method for attenuating said light beam as claimed inclaim 11 wherein the step of positioning said light vane results inapproximately three and a third percent light attenuation for a singledegree of light vane rotation into said cone shaped light beam.
 14. Themethod for attenuating the light beam as claimed in claim 11 wherein thestep of positioning of said light vane further comprises the step ofcontrolling placement of said light vane by specifying a positionranging from said zero stop position to said full stop position for saidlight vane.
 15. The method for attenuating the light beam as claimed inclaim 14 wherein the step of controlling placement of said light vanefurther comprises the step of positioning said light vane in discretepositions so as to attenuate said cone shaped light beam in f-stopincrements.